• Hong H. Pham's avatar
    sparc64: fix and optimize irq distribution · 280ff974
    Hong H. Pham authored
    irq_choose_cpu() should compare the affinity mask against cpu_online_map
    rather than CPU_MASK_ALL, since irq_select_affinity() sets the interrupt's
    affinity mask to cpu_online_map "and" CPU_MASK_ALL (which ends up being
    just cpu_online_map).  The mask comparison in irq_choose_cpu() will always
    fail since the two masks are not the same.  So the CPU chosen is the first CPU
    in the intersection of cpu_online_map and CPU_MASK_ALL, which is always CPU0.
    That means all interrupts are reassigned to CPU0...
    
    Distributing interrupts to CPUs in a linearly increasing round robin fashion
    is not optimal for the UltraSPARC T1/T2.  Also, the irq_rover in
    irq_choose_cpu() causes an interrupt to be assigned to a different
    processor each time the interrupt is allocated and released.  This may lead
    to an unbalanced distribution over time.
    
    A static mapping of interrupts to processors is done to optimize and balance
    interrupt distribution.  For the T1/T2, interrupts are spread to different
    cores first, and then to strands within a core.
    
    The following is some benchmarks showing the effects of interrupt
    distribution on a T2.  The test was done with iperf using a pair of T5220
    boxes, each with a 10GBe NIU (XAUI) connected back to back.
    
      TCP     | Stock       Linear RR IRQ  Optimized IRQ
      Streams | 2.6.30-rc5  Distribution   Distribution
              | GBits/sec   GBits/sec      GBits/sec
      --------+-----------------------------------------
        1       0.839       0.862          0.868
        8       1.16        4.96           5.88
       16       1.15        6.40           8.04
      100       1.09        7.28           8.68
    Signed-off-by: default avatarHong H. Pham <hong.pham@windriver.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    280ff974
cpumap.c 10.6 KB